The Aurora proteins are a family of three highly related serine/threonine kinases (termed Aurora-A, -B and -C) that are essential for progression through the mitotic phase of cell cycle. Specifically Aurora-A plays a crucial role in centrosome maturation and segregation, formation of the mitotic spindle and faithful segregation of chromosomes. Aurora-B is a chromosomal passenger protein that plays a central role in regulating the alignment of chromosomes on the meta-phase plate, the spindle assembly checkpoint and for the correct completion of cytokinesis.
Overexpression of Aurora-A, -B or -C has been observed in a range of human cancers including colorectal, ovarian, gastric and invasive duct adenocarcinomas.
A number of studies have now demonstrated that depletion or inhibition of Aurora-A or -B in human cancer cell lines by siRNA, dominant negative or neutralizing antibodies disrupts progression through mitosis with accumulation of cells with 4N DNA, and in some cases this is followed by endoreduplication and cell death.
FLT-3 plays an important role in the maintenance, growth and development of hematopoietic and non-hematopoietic cells. [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333 and Reilly, J T, British Journal of Hematology, 2002, 116, 744-757]. FLT-3 is a receptor tyrosine kinase which regulates the maintenance of stem cell/early progenitor pools as well the development of mature lymphoid and myeloid cells [Lyman, S, Jacobsen, S, Blood, 1998, 91, 1101-1134].
FLT-3 has been shown to play a role in a variety of hematopoietic and non-hematopoietic malignancies. Mutations that induce ligand independent activation of FLT-3 have been implicated in acute-myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), mastocytosis and gastrointestinal stromal tumor (GIST). In addition to activating mutations, ligand dependent (autocrine or paracrine) stimulation of over-expressed wild-type FLT-3 can contribute to the malignant phenotype [Scheijen, B, Griffin J D, Oncogene, 2002, 21, 3314-3333].
PDK1 (the 3-phosphoinositide-dependent protein kinase-1) plays a key role in mediating many diverse cellular events by phosphorylating key regulatory proteins that play important roles controlling processes such as cell survival, growth, proliferation and glucose regulation [(Lawlor, M. A. et al., J. Cell Sci., 114, pp. 2903-2910, 2001), (Lawlor, M. A. et al., EMBO J., 21, pp. 3728-3738, 2002)]. Many human cancers including prostate and NSCL have elevated PDK1 signaling pathway function resulting from a number of distinct genetic events such as PTEN mutations or over-expression of certain key regulatory proteins [(Graff, J. R., Expert Opin. Ther. Targets, 6, pp. 103-113, 2002), (Brognard, J., et al., Cancer Res., 61, pp. 3986-3997, 2001)]. Inhibition of PDK1 as a mechanism to treat cancer was demonstrated by transfection of a PTEN negative human cancer cell line (U87MG) with antisense oligonucleotides directed against PDK1. The resulting decrease in PDK1 protein levels led to a reduction in cellular proliferation and survival (Flynn, P., et al., Curr. Biol., 10, pp. 1439-1442, 2000).
Protein kinases are attractive and proven targets for new therapeutic agents to treat a range of human diseases, with examples including Gleevec and Tarceva. The Aurora, FLT-3, and PDK1 kinases are especially attractive due to their association with numerous human cancers and the roles they play in the proliferation of these cancer cells. Therefore, there is a need for compounds that inhibit protein kinases.